Image forming devices, such as a color page printer, a photocopy machine and a multifunction machine, conventionally includes a power saving function. These image forming devices control power consumption by terminating power supply to a thermal fuser that consumes a large amount of electricity and by shifting to a power saving mode when print data is not received from a higher-level device, such as a computer, after elapsing a power saving mode shifting time, which is preset in advance, after completion of a print operation.
Such a technique is disclosed in Japanese Laid-Open Patent Application Publication No. 2004-101919 (herein, JP 2004-101919). According to JP 2004-101919, the image forming device includes means to recognize a day of the week and time and, for such a day of the week and the time, sets a long power saving mode shifting time for a time period with a high usage frequency and a short power saving mode shifting time for a time period with a low usage frequency.
However, in the conventional image forming device described in JP 2004-101919, there is a problem that the power saving mode shifting time continues to be set long even when the actual usage frequency decreases during the time period, in which the usage frequency is assumed to be high, causing unnecessary power consumption. In addition, there is a problem that the power saving mode shifting time continues to be short when the usage frequency coincidentally increases during the time period, in which the usage frequency is assumed to be short, causing the time for the printing to start to be unnecessarily long.